New CRAN warnings on STRING_PTR and VECTOR_PTR

[eddelbuettel]

Running a recent r-devel:

• checking compiled code ... NOTE
  File ‘Rcpp/libs/Rcpp.so’:
  Found non-API calls to R: ‘STRING_PTR’, ‘VECTOR_PTR’

Compiled code should not call non-API entry points in R.

See ‘Writing portable packages’ in the ‘Writing R Extensions’ manual,
and section ‘Moving into C API compliance’ for issues with the use of non-API entry points.

• checking sizes of PDF files under ‘inst/doc’ ... OK

The new section Moving into C API compliance mentions read-only variants STRING_PTR_RO and VECTOR_PTR_RO which look promising.

[kevinushey]

I can take a gander.

[eddelbuettel]

That would be sweet. I am a little tied up right now but should have time a little later.